Abstract The Hellenic shelf lies within and around the Aegean microplate, which is one of the world's most seismically active areas, and has experienced extreme tectonism throughout Quaternary time. This activity, together with eustatic sea-level changes and water-circulation patterns over the same time period, controls the overall configuration of the Hellenic shelf, the rates of uplift and subsidence, and determines the sediment supply and depot centre, as well as the sediment-transfer processes. The above-mentioned geological processes are the causative factors for the frequent occurrence of a variety of geological hazards, such as active faults, submarine gravitational mass movements, tsunami and active gas seeping from the seabed.

Abstract In this paper we review the main, long- and short-term geological and geotectonic processes that have controlled the development of Pleistocene landscapes in the Aegean region above and below the fluctuating sea level. We discuss the potential for further research on reconstruction of submerged landscapes of the continental shelf and beyond with the aim of addressing questions concerning Palaeolithic settlement. The geological, tectonic, morphological and hydrogeological background provides information for the assessment of the natural resources available to hominins. Along with the palaeogeographical evolution of the shallow coastal and shelf areas, they are examined in parallel with the terrestrial archaeological record in order to open windows to future work in a region that has remained marginal to human origins research. On the basis of the multi-variable tectonic evolution and geomorphological configuration of the coastal and shelf areas, we propose to divide the Aegean region into nine geographical units, each with its own geotectonic and morphological history and traits. These units can be further grouped to provide larger neighbouring and culturally meaningful regions, suitable for archaeological analysis, or subdivided to provide smaller target areas in which to work.

In the Aegean area, distinct fault patterns with their associated stress regimes are evidenced along a curved convergent plate boundary. In this article, we analyze and review late collisional and extensional structures in five structural regions along the External Hellenides orogenic belt in order to define, primarily, the evolution of onshore basins and, secondarily, the evolution of off-shore basins and the role of the inherited structures within the present geotectonic framework. We also evaluate how these structures act on seismicity as well as present-day motion and magmatism in the Aegean area. Northwestern Greece, which corresponds to our Region I, represents an area of active continental collision in which a previously overthickened crust collapsed mainly parallel to the structural grain of the orogen. At present, the most active structures in this region are the northwest-trending thrusts and the northeast-trending normal faults. Strong coupling and the transmission of horizontal forces from the collision front appear to explain the deformation within this region. Central Greece (Region II) displays a mixed type of contractional-extensional deformation. Mesozoic inherited transverse structures are reactivated as WNW-trending faults and appear to accommodate most of the active north-south-trending present-day extension. Deformation in this area appears to be controlled both by rollback of the subducting slab and by the lateral extrusion of the Anatolia plate. The areas that spread along the more curved parts of the Hellenic arc (Regions III and V) well emphasize the control exerted by pre-existing northeast-trending structures as well as their long-lived activity during the evolution of the arc. Present deformation within these regions possibly reflects the oblique convergence process, which is occurring in both areas in different degrees. Finally, analysis of deformation patterns in the central part of the Hellenic arc and the Aegean Sea (Region IV) suggests that almost all pre-existing structures have remained active until the present and accommodate extensional deformation and rapid motion through a nonorthogonal fault system that crosscuts a thin and thermally weakened continental crust. Deformation north of our Region IV is accommodated primarily by the North Aegean trough. Basin-bounding faults within the North Aegean trough are dominantly characterized by apparently normal components as well as strike-slip components. Plate boundary conditions, as well as pre-existing structures with a favorable orientation relative to the current crustal motion, control and variably affect the present-day deformation along the Hellenic arc and trench system.

Abstract The Kythira–Antikythira strait, within the SW Hellenic Arc, forms a 100 km long NNW–SSE trending ridge between Peloponnesus and Crete and represents the submarine continuation of the Hellenic Alpine belt. In order to present the shallow as well as the deeper structure of Kythira–Antikythira strait we studied five seismic sections, oriented either parallel or perpendicular to the inner part of the Hellenic Arc. This information was complemented with velocity analyses from a dense network of seismic lines and information concerning the bathymetry. Contractional structures recognized on the seismic profiles indicate that this part of the Gavrovo–Tripolitza geotectonic zone was involved in the Miocene shortening related to the westward propagation of the Hellenic fold-and-thrust system. East-dipping thrust faults which root in the top of the crystalline basement were identified on the seismic profiles. The deepest reflector identified on the profiles corresponds to the crystalline basement. Shallower reflectors include those corresponding to the contacts between the Mesozoic/Miocene, Upper Miocene/Lower Pliocene and Pliocene/Pleistocene sedimentary sequences. The Upper Cenozoic to Quaternary sequence rests unconformably upon Mesozoic carbonates. Messinian intrusions, forming small scale domes, deform the Pliocene–Quaternary sedimentary succession. West- and east-dipping normal faults were also recognised both within the Palaeozoic and Cenozoic successions, and are related to regional extension during sedimentation.

Abstract Historical tsunamis and tsunami propagation are synthesized in the Eastern Mediterranean Sea region, with particular attention to the Hellenic and the Cyprus arcs and the Levantine basin, to obtain a better picture of the tsunamigenic zones. Historical data of tsunami manifestation in the region are analysed, and compared with current seismic activity and plate interactions. Numerical simulations of potential and historical tsunamis reported in the Cyprus and Hellenic arcs are performed as case studies in the context of the nonlinear shallow-water theory. Tsunami wave heights as well as their distribution function are calculated for the Paphos earthquake of 11 May 1222 and the Crete earthquake of 8 August 1303 as illustrative examples depicting the characteristics of tsunami propagation, and the effects of coastal topography and near-shore amplification. The simulation studies also revealed that the long-normal distributions are compatible with reported damage. Furthermore, it is necessary to note that high-resolution bathymetry maps are a crucial component in tsunami wave simulations, and this aspect is rather poorly developed in the Eastern Mediterranean. The current study also demonstrates the role of bottom irregularities in determining the wave-height distribution near coastlines. Assuming the probability of occurrence of destructive tsunamigenic earthquakes, these studies will help us to evaluate the tsunami hazard for the coastal plains of the Eastern Mediterranean Sea region. We suggest that future oceanographic and marine geophysical research should aim to improve the resolution of bathymetric maps, particularly for the details of the continental shelf and seamounts.